The proposed work is the next logical step in a collaboration on childspacing that has resulted in 4 papers to date. It seeks to explicate observed differentials in birth intervals in terms of differences in breastfeeding and contraception. The methodology follows life-table logic by examining the probability of birth in successive duration segments of an interval, given "survival" to each segment. This procedure is chosen over proportional hazards because contraception and breastfeeding (and thus their major determinants) are likely to have effects concentrated at certain durations. Analyses will be specific to second, third, fourth through eighth intervals. Breastfeeding will be included in the analysis of each interval segment in a way that avoids simultaneity with length of birth interval. There are three objectives. The first is an examination of the determinants of breastfeeding and contraception and of the role these differentials play in observed differences in the pace of fertility using the detailed contraceptive and breastfeeding histories for the Korean world fertility survey. The second objective is to evaluate the consequence of the common WFS restriction of breastfeeding and contraceptive data to the last closed and open intervals, and the omission of breastfeeding data for intervals including a current pregnancy. These omissions result in a substantially biased sample of intervals. For this objective we will artificially impose the WFS constraints on the complete Korean histories and examine the nature of the resulting biases. The third phase will be a pooled analysis of 5 Asian countries: Korea, Thailand, Malaysia, Philippines and Sri Lanka. WFS raw data tapes will be obtained to provide information on intervals with current pregnancies, and the lessons of phase two will guide the selection of the appropriate sample to avoid biases from the focus on last closed and open intervals. The same type of analysis described for phase one will be pursued except that important differences between country and ethnicity groups will also be explored.